Accurately attaching a lens to a light source such as to the core of an optical fiber is of critical importance in many applications of fiber optics, including optical communications and medicine. For example, the ease and efficiency of the coupling of light into and out of an optical fiber can be greatly improved if an appropriate lens is attached to the fiber. In communication systems, an external lens added to a fiber can be used to focus output light onto a smaller and faster detector, thus increasing the ultimate speed of the system. A lens-affixing technique would also be advantageous in other areas, such as biological or medical applications, where the accurate delivery of a small, intense beam spot is required. In all of these applications, performance is enhanced as the alignment of the optical center of the lens with an intensity maximum of the fiber is improved.
Several methods are currently available to align a lens with a laser or an optical fiber including mechanical methods, laser ablation, and the use of surface tension forces. U.S. Pat. Nos. 4,818,053 and 4,079,404 describe support structures, or an "optical bench", for aligning optical components such as lasers, lenses, and optical fibers. U.S. Pat. No. 4,867,521 describes a mechanical method for mounting a lens on a glass plate and then mounting an optical fiber in relation to the lens and glass plate such that the emerging light is collimated. The alignment of the fiber with the glass plate and the lens is determined by monitoring the emitted light with a photodetector, while adjusting the position of the plate relative to the lens until the maximum output is produced. The elements are then fixed in place with a UV-curable adhesive. U.S. Pat. No. 4,932,989 describes the fabrication of microlenses on optical fibers through the use of a pulsed laser beam to ablate the end portion of a fiber.
A method has also been described for centering a lens on an optical fiber using the surface tension of an adhesive that has been applied to the fiber (Dakss et al., 1980, Electronics Lett., Vol 16, pp. 463-464). In this method the adhesive is applied to the fiber tip, and a micromanipulator and a low power microscope are used to aid in the centering of the fiber over a spherical lens. The fiber is lowered so that the adhesive contacts the lens. The surface tension of the adhesive then moves the lens to the center of the fiber core, and the adhesive is cured. This method permits centering of a lens on the fiber core with an accuracy of only approximately 3 microns.
It is desired to achieve an inexpensive, simple and reliable method that improves the accuracy of the centering of lenses upon optical fibers and other light sources having an intensity maximum.